/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.accept;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Locale;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;

import org.springframework.http.MediaType;
import org.springframework.lang.Nullable;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

/**
 * An implementation of {@code MediaTypeFileExtensionResolver} that maintains
 * lookups between file extensions and MediaTypes in both directions.
 *
 * <p>Initially created with a map of file extensions and media types.
 * Subsequently subclasses can use {@link #addMapping} to add more mappings.
 *
 * @author Rossen Stoyanchev
 * @since 3.2
 */
public class MappingMediaTypeFileExtensionResolver implements MediaTypeFileExtensionResolver {

    private final ConcurrentMap<String, MediaType> mediaTypes = new ConcurrentHashMap<>(64);

    private final MultiValueMap<MediaType, String> fileExtensions = new LinkedMultiValueMap<>();

    private final List<String> allFileExtensions = new ArrayList<>();


    /**
     * Create an instance with the given map of file extensions and media types.
     */
    public MappingMediaTypeFileExtensionResolver(@Nullable Map<String, MediaType> mediaTypes) {
        if (mediaTypes != null) {
            mediaTypes.forEach((extension, mediaType) -> {
                String lowerCaseExtension = extension.toLowerCase(Locale.ENGLISH);
                this.mediaTypes.put(lowerCaseExtension, mediaType);
                this.fileExtensions.add(mediaType, lowerCaseExtension);
                this.allFileExtensions.add(lowerCaseExtension);
            });
        }
    }


    public Map<String, MediaType> getMediaTypes() {
        return this.mediaTypes;
    }

    protected List<MediaType> getAllMediaTypes() {
        return new ArrayList<>(this.mediaTypes.values());
    }

    /**
     * Map an extension to a MediaType. Ignore if extension already mapped.
     */
    protected void addMapping(String extension, MediaType mediaType) {
        MediaType previous = this.mediaTypes.putIfAbsent(extension, mediaType);
        if (previous == null) {
            this.fileExtensions.add(mediaType, extension);
            this.allFileExtensions.add(extension);
        }
    }


    @Override
    public List<String> resolveFileExtensions(MediaType mediaType) {
        List<String> fileExtensions = this.fileExtensions.get(mediaType);
        return (fileExtensions != null ? fileExtensions : Collections.emptyList());
    }

    @Override
    public List<String> getAllFileExtensions() {
        return Collections.unmodifiableList(this.allFileExtensions);
    }

    /**
     * Use this method for a reverse lookup from extension to MediaType.
     *
     * @return a MediaType for the key, or {@code null} if none found
     */
    @Nullable
    protected MediaType lookupMediaType(String extension) {
        return this.mediaTypes.get(extension.toLowerCase(Locale.ENGLISH));
    }

}
